The present invention relates to a heat-resistant inorganic composition or, more particularly, to a heat-resistant composition useful as a coating material which is capable of being firmly and adhesively bonded to the surface of metals, such as iron, copper, silver, etc., and inorganic materials, such as glass, etc. The inventive composition is also useful as an adhesive agent for bonding metals or for bonding a metal and an inorganic fiber or a ceramic material such as a refractory, glass, etc.
In the prior art, various attempts have been made to develop a heat-resistant inorganic coating composition containing metals for preventing the oxidation and for improving the heat conductivity of trays, which are used in firing ceramic products and carbonaceous articles. Also, attempts have been made to develop a coating material for preventing corrosion of steel-made heat exchangers at high temperatures.
In particular, attempts have been made to coat the surface of a ceramic article with a metal in order to utilize the electric and thermal characteristics inherent in metals. Also, attempts have been made to obtain an adhesive bonding between graphite and metal or between glass and metal. Coating of the surface of a ceramic article with a metal has, however, only been performed with great difficulties. Known methods for providing a metallic coating onto the surface of a ceramic article include the methods of, for example, spray fusion, chemical vapor deposition (CVD), metal ion migration, electroless plating, vacuum deposition, sputtering, ion brazing and the like.
These methods are, however disadvantageous due to the difficulties of their various coating procedures, which difficulties are especially apparent in the coating of large articles. Accordingly, from an industrialization point of view, the known methods of providing a metal coating on a ceramic substrate have not been satisfactory.
The adhesive bonding of the metal, such as iron, copper, silver and the like, and a ceramic, ceramic fibers, glass and the like, on the other hand, has been usually performed by use of a solder glass. The problems in soldering with solder glass are the necessity of maintaining a high temperature of 400.degree. to 500.degree. C. or higher. The use of a solder glass is also extremely difficult when bonding of an article of a complicated form or large size, as well as in the bonding of ready-built materials. Therefore, the possibility of performing the soldering at lower temperatures has been investigated. However, these investigations have not developed practically satisfactory results. Moreover, solder glass has the undesirable characteristic, especially when bonding metals together, that the desirable properties of the bonded metals are less. Accordingly, the adhesive bonding of metals has been desirably performed by the use of an adhesive agent composed of the same type of metals to be bonded, in order to retain the inherent properties of the bonded metals.
Known heat-resistant metal-containing inorganic adhesives materials include a coating composition comprising zinc silicate which is capable of being coated on an iron surface which is resistant to temperatures of up to 540.degree. C., and a coating composition composed of powders of metallic aluminum and iron (III) oxide (see, for example, Japanese Patent Kokai 55-5167 and Material Performance, May, 1975, page 25-29).
Hitherto, there has not been known a metal-containing heat-resistant inorganic composition having the desirable properties that it is capable of being coated on a metal surface or an inorganic material surface, that it can be used as an adhesive agent between metals or between a metal and a ceramic material, that it can provide such a firm bond so as to withstand heating at elevated temperatures in a range up to 800.degree. C. or higher and that it is capable of being easily worked or used within conventional coating or bonding processes.